X-ray Microscopy Observation of CFRP with Synchrotron Radiation

This study reviews synchrotron-radiation X-ray microscopy observation applied to carbon-fiber-reinforced plastics (CFRP), focusing on multiscale crack initiation, propagation, and chemical states of carbon. (1) In situ and operando observations of CFRP under various types of loading using an X-ray microscope (Nano SR X-CT) successfully revealed that with a spatial resolution of ＜50 nm, cracks were initiated at the interface between the carbon fibers and epoxy resin and propagated along the interface, and some cracks branched into the resin. The detailed behavior was affected by the triaxial stress state near the crack tip. (2) Topological data analysis using persistent homology was applied to quantitatively evaluate the crack shape, thereby identifying the crack initiation point in 3D space. (3) The carbon chemical states at the carbon fiber/epoxy interface were investigated using a scanning transmission X-ray microscope, indicating that the σ and π bonding states at the interface differed from those in the carbon fiber or epoxy.